1. Field of the Invention
This invention relates to a positive temperature coefficient (PTC) polymer composition and a material made therefrom, more particularly to a PTC conductive polymer composition comprising a non-ionic copolymer of a substituted or non-substituted olefin monomer and an anhydride monomer.
2. Description of the Related Art
A positive temperature coefficient (PTC) element exhibits a PTC effect that renders the same to be useful as a protecting device, such as a fuse. The PTC element includes a PTC polymer material and first and second electrodes formed on two opposite surfaces of the PTC polymer material. The PTC polymer material includes a polymer matrix that contains a crystalline region and a non-crystalline region, and a conductive particulate filler that is dispersed in the non-crystalline region of the polymer matrix and that is formed into a continuous conductive path for electrical conduction between the first and second electrodes. The PTC effect is a phenomenon that when the temperature of the polymer matrix is raised to its melting point, crystals in the crystalline region start melting, which results in generation of a new non-crystalline region. As the new non-crystalline region is increased to an extent to merge into the original non-crystalline region, the conductive path of the conductive particulate filler will become discontinuous and the resistance of the PTC polymer material will be sharply increased, thereby resulting in an electrical disconnection between the first and second electrodes.
The PTC element is required to have a high PTC effect, a high conductivity, and a high electrical stability. In addition, the polymer matrix of the PTC element is required to have a strong adhesion to the first and second electrodes.
Although the conductivity of the PTC polymer material can be improved by increasing the amount of the conductive particulate filler, the PTC effect and the adhesion of the polymer matrix to the first and second electrodes are decreased correspondingly.
It has been proposed in the art that the adhesion of the polymer matrix to the first and second electrodes can be enhanced through the use of a grafted olefin polymer, such as maleic anhydride-grafted polyethylene. The maleic anhydride group of the grafted olefin polymer and the first and second electrodes form polar-polar interactions thereamong, thereby enhancing the adhesion of the polymer matrix to the first and second electrodes and preventing undesired peeling of the first and second electrodes from the polymer matrix. Although the polymer matrix containing the grafted polymer can provide the aforementioned advantage, it can result in a significant decrease in the conductivity of the PTC polymer material.